With the increased incidence of obesity, Type 2 diabetes has become one of the foremost public health problems in the developed world. Despite decades of research dedicated to developing treatments for type 2 diabetes, the inefficacy, side effects, and adverse events of most therapies demand novel treatments. Glucose homeostasis is tightly regulated by insulin and the counter regulatory hormone glucagon, secreted by pancreatic -cells and a-cells, respectively. The dysregulation of glucose homeostasis in T2DM results from reduced glucose clearance coupled with increased hepatic glucose production. Because glucagon potentiates hepatic glucose production, while inhibiting adipose tissue glucose clearance, it is increasingly appreciated as an important target to treat T2DM. In fact, suppression of glucagon signaling or secretion is therapeutically beneficial for T2DM. While inhibition of glucagon signaling limits the deleterious effects of hyperglucagonemia, complete blockade of glucagon receptor signaling results in metabolic pathophysiologies, such as hepatic steatosis and vascular events. An ideal glucagon-targeted treatment would allow for nutrient responsive alterations in glucagon secretion, while preventing the hyperglucagonemia of obesity. a-cell mitochondrial function is an important and, thus far, unexplored target to modulate glucagon secretion while maintaining nutrient responsiveness. Pancreatic a- and -cells are sensitive to glucose induced changes in the ATP:ADP ratio. In the a-cell, glucose-stimulated increases in cellular ATP decrease cytoplasmic Ca++ and inhibit the release of glucagon. In the -cell, glucose stimulated increases in cellular ATP increase cytoplasmic Ca++ and encourage insulin release. As such, the role of ATP generation in the regulation of glucoregulatory hormones is of primary importance. In this application, I propose to utilize 2 innovative models that allow for cell-type specific modulation of mitochondrial function to test 2 aims. Aim 1: Assess the impact of graded levels of a-cell mitochondrial dysfunction on glucose homeostasis in the chow fed mouse. Aim 2: Test the effects of enhancing a-cell mitochondrial function on glucose homeostasis in a mouse model of type II diabetes. I expect this study to allow us to quantify the specific effects of hyperglucagonemia both in the presence and absence of hyperinsulinemia. With these studies, I intend to identify the possible therapeutic benefits associated with increasing mitochondrial ATP generation to suppress a-cell glucagon secretion and improve whole-body glucose homeostasis in a mouse model of type II diabetes. Moreover, the studies proposed in this grant will establish that a-cell mitochondria are a valid target to safely treat Type 2 diabetes mellitus.